Diaphragm for acoustic instruments



Jan. 16, 1923.

H. L. DUNCAN.

DIAPHRAGM FOR ACOUSTIC INSTRUMENTS.

FILED MAY 9, I919.

5 noemtoz Patented Jan. 16, 1923.

UNITED STATES HARRY L. DUNCAN, OF MAHWAH, NEW JERSEY.

DIAPHRAGM FOR- AQOUSTIC INSTRUMENCTS.

Application filed May 9, 1919.

T all whom it may concern:

Be it known that I, HARRY L. DUNCAN, a citizen of the UnitedStates, and resident of Mahwah, county of Bergen, State of New Jersey, have made a certain new and useful invention Relating to Diaphragms for Acoustic Instruments, of which the following is a specification, taken in connection with the accompanying drawing.

This invention relates especially to diaphragms for acoustic instruments, such as phonographs, telephones, etc. in which the diaphragm is preferably formed of fibrous material such as the desired number of thicknesses of suitable cotton cloth, cotton batting or other fibrous material carrying and preferably quite thoroughly impregnated with relatively large proportions of cured phenolic condensation cementing material, such as bakelite, condensite or redmanol varnish compositions. By using woven cotton or other fabric a relatively uniform thickness layer of fibrous material may be conveniently secured which has sulficient freedom of movement between the fibres so as to have considerable. diagonal flexibility or stretching properties so as to form coned up or other warped surfaces especially when the fabric is coated and impregnated with the heated phenolic condensation cementing material which seems to promote the uniform stretching of the threads which are preferably loosely twisted. Large acoustic diaphragms of a foot or more diameter may be conveniently formed of such material and thecentral'portion of the diaphragm may in many cases be given ample stiffness and strength by forming a coned up, corrugated or other warped surface therein which prevents undesirable local yielding. The relatively yieldable edge portions of the diaphragm may be of relatively fiat contour so that the vibration of the stiffened diaphragm center causes bend- Serial No. 296,620.

Any suitable strong fibrous material may be used for large diaphragms of this character in connection with suitable incorpo rated phenolic condensation cementing material, the fibrous material for best results being such as is not undesirablyaflected by the cementing material used or by the (111.1 ing heat to which it is subjected, w'hichior rapid pressure molding and curing action is usuall about 300 to 320 Fahrenheit or so for fifteen to thirtyminutes or thereabouts, although, if desired, a considerably reduced curing heat may be used if acting for a correspondingly lon er time. Tll fibrous material should also ave sufiicientl long fibre to give the desired strength and coherence during the pressure curingor molding operation where considerable distortion of the previously formed or treated blank of fibrous material occurs at this'time and of course lon 'er fibre gives greater strength to the finished article, although the cementing action of'the bakelite or other phenolic condensation cementing K131181121} naturally cements or unites the fibres to-' gether and gives them greatly increased strength under these conditions. For many purposes muslin or other closely .woven cotton fabric of which the-threads are preferably of substantially uniformstrength in each direction and in which the threads are preferably loosely twisted is desirable for this purpose and in some cases the fabric may with advantage be a napped' fabric which somewhat increases the uniform distribution of the superficial 'fibres and affects a somewhat greater subdivision of the in-- .corporated phenolic condensationcementmg material. Muslin having a count of sixty to eighty threads or so per linear inch in both directions, which may, for example, be. impregnated so as to contain forty to permit considerable distortion such as occurs in forming coned up or stiffened diaphragm centers of this character so that the diaphragm with or without such wavy edge portions may be reliably produced and relatively constant shape, strength and other properties secured when the same number of thicknesses of similarly impregnated fabric are used in eachcase. As an illustrative example light muslin two to six ounces per yard may be heavily coated and impregnated with suitable bakelite or condensite varnish compositions and dried and also preferably slightly cured in the drying process so as to minimize undersirable melting or flowing of the phenolic condensation cementing material under the pressure heat curing treatment. Several layers of such impregnated fabric may be used in forming a diaphragm ten to twenty inches in diameter more or less and the fabric may be yieldably supported and somewhat stretched above the heated metal faced mold which may be used so that the coned up or corrugated molding members uniformly extend or distort the central portions of the fabric blanks so as to form a substantially uniform layer of material in which the cured phenolic, condensation cementing material forms a. continuous and impervious surface on both sides and strengthens and unites the embedded-threads which are more or less uniformly distributed throughout the material. One or more layers of such stiff and rather rigid impregnated fabric may be warmed and softened so as to be quite flexible and when yieldingl supported at the corners of a square blan for instance, the. central portion of the yielding fabric can be forced out transversely into generally conical or v projecting shape so as to project in some instances as far beyond the plane of the edges as twenty or thirty percent or more of the original width of the blank withoutnecessarily causing folding or puckering of the edge portions or breaking or tearing of the fabric if a good grade of cotton fabric is used having loosely twisted or loosely woven threads.

lit is thus unnecessary with such proportions of coned up or corrugated stifiened centers as are shown to preliminarily shape up or tailor a blank, as 'by cutting out or fitting together sector shaped pieces of cloth or paper, since by stretching one or more layers o'f'yieldable fabric of this char acter all such preliminary shaping operations are avoided and also a much more" de sirable and uniform stiffened diaphragm structure simultaneously secured Furthermore, by usin continuous layers of such fabric and. stiffening the diaphragm by its arched'up or projecting shape instead of by additional layers or thickness of material, it is possible to avoid the difficulty of accurately positioning the fabric blanks and additional central stiffening layers which is especially undesirable when simultaneously molding a large number of small diaphragms. This stretching of the center simultaneously draws in the edges of the diaphragm material to some extent so that in some cases the edge portions around the periphery of the finished diaphragm contain a relatively greater proportion, of fibrous material as compared to the central portions of the diaphragm and this is sometimes advantageous because such more cause containing less of this incorporated phenolic condensation cementing stiffening materiaL The form of diaphragm shown in Fig. 1 may be advantageously produced from one or more sheets of such impregnated cloth or other suitable fibrous material, the projecting stiffened center portion 3 being coned up gradually as indicated so as to project beyond the diaphragm body 1. Thi coned up or stiffened center portion may merge gradually into the body or edge portions 1 of the diaphragm and an intermediate gradually curved portion 2 of greater or less extent-may be formed at this part of the diaphragm to give a gradually increasing degree of flexibility under transverse vibration; The extent of the coned up or center portion 3 may of course be varied under different conditions and may comprise as indicated in Fig. 1 somewhatmore than half of the total diameter of the diaphragm in the case of relatively small diaphragms' having a diameter of two to eight inches moreor less, although for relatively larger waves therein having high spots 15 and interposed low spots 14, the planes of which may be a sixteenth to an eighth of an inch or so apart transversely of the plane of the I about thirty degree angles givinggood re-" diaphragm in the case of relatively small diaphragms not more than, say, six inches in diameter. The sinusoidal or other wavy form of the diaphragm edge may advantageously be yieldingfly clamped or mounted between any suitable form of elastic or yielding clamping supporting surfaces such as circular or flat sectional rings or gaskets of vulcanized rubber, soft paper or the like, so that the wavy edge portion is somewhat flattened or forced into more nearly flat position so that a fairly definite degree of poripheral elongation is thus secured which tends to increase the diameter of this edge portion of the diaphragm and simultaneously exert a corresponding radial tension on the inner portions of the diaphragm which is desirable for many purposes because securing increased pitch and more reliable vibration in response to various impulses.

Fig. 2 shows another form of diaphragm in which the coned up or stiffened central portion 4 is of relatively greater extent and may as indicated have a diameter of eight tenths or more of the total diameter of the diaphragm in the case of some'relatively elements or portions of this stiffened center.

may make angles of twenty to forty degrees or so with the plane of the diaphragm edge,

- sults. Also for 'greater stiffness this coned up or projectin the case of the Fig. l diaphragm have concave edge sections or radial elements as indicated so as to form a more definitely warped surface having still greater trans- .verse rigidity than a cone of approximately equal pitch. The edge portion 6 of the diaphragm may be fiat or provided with edge flutes or wavy portions, such as 14, 15,

of which a dozen or more may be provided in the case of such large diaphragms so that suflicient radial tensioning can be secured without having undesirable transversely displaced edge portions which might be undesirable in connection with the ordinary mounting or supporting means employed. It is not, however, necessary in all cases to use such fluted edge portions and as'seen in Fig. 3 the edge portions 7 may be substantially flat and may gradually merge into the coned up stiffened center portion 8 by an intermediate curved connecting portion 9 to central portion may as in give a gradual transition between the relatively stiff center and the flat more yielding edges. Diaphragms of the general types illustrated may be conveniently formed as above described from any suitable inpregnated, thin, yieldable woven, braided or knit fabric of cotton, linen or silk, etc. and may in some cases have a diameter of nine to twelve inches or more; and good results are secured where such a diaphragm contains relatively high proportions of quite thoroughly cured and correspondingly stiff and strong phenolic condensation cementing material, such as bakelite varnish compositions which may be present in the finished diaphragm to the extent of sixty to eighty percent or more in some cases, seventy percent of such material by weight giving good results. Bakelite or other phenolic condensation cementing material is highly desirable for this purpose because of its relatively light weight and strong and elastic properties under such slight amplitude vibrations as are used in acoustic apparatus, and in some cases especially for articulate speech and the like still less proportions of fabric or other fibrous materialmay be used where there is correspondingly less danger of accidental breakage or sudden stresses. The phenolic condensation cementing material may be conveniently formed insubstantially uniform thickness layers by im pregnating or coating thin cloth or similar fabric therewith and then preferably quite thoroughly drying and partly curing the phenolic condensation cementing material. so that during the preliminary shaping at least undesirable melting does not occur. Furthermore, the presence of the incorporated fibrous material in the cured phenolic condensation cementing material greatly toughens and strengthens the same against fracture because the interposed .fib'res with which-the cementing'material which may comprise the corrugations 11,

12, of which any desired number may be used, a gradually curved portion 10 being formed, if desired, between this corrugated somewhat stiffened portion and the main coned up stiffened center. Fig. 5 shows still another form of construction which may be advantageously used where the diaphragm center 14 is to be located in substantially the plane of the diaphragm edges 15. In this case a number of angularly arranged corrugated or reversely conical portions may be interposed between the central and edge portions and the corrugated edges 16, 17 and 18 may be formed in this way which may, if

. desired, have equal transverse extent -on either side of the central or edge portions or both. Any desired number of. such angular corrugations which may have some such angle as twenty or thirty degrees more or less from the plane of the diaphragm edges may be used for such stiffening purposes and it is usually desirable to have the edges of such corrugations somewhat stiffened and strengthened byso molding the one or more layers of impregnated fabric that a greater proportion of the phenolic condensation stiffening and strengthening material is present at these connecting edge cor-- rugations. Of course 'in' any of these different shaped diaphragms the thickness of the material may be regulated to correspond with the intended service of the diaphragm and by using the desired number. of layers of proper thickness fabric this may be very readily and effectively secured. For instance, a single thickness of two ounce muslin heavily impregnated with dried phenolic condensation cementing material may be cured unde such heat and high pressure of a number of hundred pounds per square inch as to secure substantially uniform thickness walls of the diaphragm structure and not more than three or four thousandths of an inch thick in the case of light diaphragms.

By using a number of layers of this 'material the wall thickness may be correspondingly increased or in some cases a single layer of heavier; fabric up tomuslin six or eight ounces per square yard and preferably having a nappe'd surface may produce a thickness of the cured diaphragm Wall of twelve to sixteen thousandths of an inch or so when corresponding proportions of phenolic condensation cementing material are used in the original impregnated fabric.

This invention has been disclosed in -con-.

nection with a number of illustrative embodiments, forms, proportions, elements, parts, shapes, materials, compositions,- conditions, and methods of preparation, proaaaait ing material to the extent of between about seventy and eighty percent by weight of the diaphragm. a

-2. The acoustic diaphragm having a diameter of more' than eight inches and com- 7t prising a stiffened coned up center portion 0 and a relatively-flat yielding edge portion, said diaphragm being formed of a continuous layer of, fabric carrying incorporated cured phenolic condensation cementing material to the extent of over fifty percent by weight of the diaphragm.

3. The acoustic diaphragm comprising a stiffened non-planiform center'portion, saiddiaphragm being. formed of a single continuous layer of cloth carrying incorporated cured phenolic condensation cementing material to the extent of more than sixty percent by weight of the diaphragm.

4. The acoustic diaphragm havingadiameter of .more' than eight inches and comprising a relatively yielding edge portion and a substantially conical stiffened center portion constituting at least seventy percent of the diaphragm diameter, said diaphragm being formed of cotton fiber carrying a large proportion of incorporated cured'phenolic condensation cementing and stiffening material.

'5. The acoustic diaphragm comprising a relatively yielding edge portion and a pro: jecting stiffened center portion constituting at least half of the diaphragm diameter, said diaphragm being-formedof fiber carrying a large proportion of incorporated 1 cured phenolic condensation cementing and stiffening material.

6. The acoustic diaphragm over eight inches in diameter formed of a single layer of fabric impregnated with at least an equal weight of. cured phenolic condensation cementing material said diaphragm having a substantially uniform thickness of not more than a hundredth of an inch through out its vibrating portions and comprising projecting non portions. r

7. The acoustic diaphragm over eight inches in diameter formed of fabric carryplaniform stiffened central ing cured phenolic condensation cementing material, said diaphragm having a substantially uniform thickness of not more than a hundredth of an'inch throughout its stiffened vibrating portions and, 'comprising projecting stifiened central portions.

8. The substantially uniform thickness acoustic diaphragm having a stiffened nonplaniform central vibrating portion and a relatively yielding ,edge portion, said diaphragm being formedof 'a single layer of 1 5 fabric carryingincorporated strong hard-- ened resinous cementing material to the extent of at least seventy percent by weight of the diaphragm in its 'vibrating'portion.

9. The diaphragm having a stiffened non-planifori'n central vibrating portion and a relatively yielding edge portion, said diaphragm being formed of fabric carrying incorporated strong hardened resinous cementing material to the extent of at least fifty percent by weight of the diaphragm in its vibrating portion.

10. The acoustic diaphragm comprising a continuous layer of fabric impregnated With cured phenolic condensation cementing material, said diaphragm having stiffened' central portions of non-planiform projecting contour comprising elements arranged at an angle of at least twenty deg'ees from the plane of the diaphragm e ge.

11. The acoustic diaphragm comprising a substantially continuous. layer of thin woven cotton fabric impregnated with at least an equal weight of cured phenolic. condensation cementing and stiffening material, said diaphragm comprising stiffened projecting central portions arranged at angles of over twenty five degreesfrom the plane of the diaphragm edge. e

' 12. The diaphragm comprising a substantially continuous layer of thin Woven fabric impregnated with cured phenolic condensation cementing and stiffening material, said diaphragm comprising stiffened projecting central portions-arranged at angles'of over twenty degrees from the plane of the diaphragm edge and extendihg transversely from said plane to a distance more than twenty percent of the diaphragm diameter.

13. The acoustic diaphragm over ten inches in diameter and having aprojecting stiffened Warped surface central portion and increasingly flexible flattened edge portions, said diaphragm being formed of fabric carrying over sixty percent by Weight of incorporated cured phenolic condensation cementing material forming a substantially" impervious diaphragm surface.

14-. The acoustic diaphragm having a stiffened Warped surface central portion and increasingly flexible edge portions, said diaphragm being formed of fibrous material carrying over sixty percent by weight of incorporated-cured phenolic condensation cementing material. I

15. The acoustic diaphragm formed of a single continuous layer of Woven cotton fabric carrying cured phenolic condensation cementing material, said diaphragm comprising stiffened vibrating portions of nonplaniform substantially conical projecting contour and having substantially uniform thickness of not more. than six thousandths of an inch throughout its stiffened vibrating portions. 4

16. The acoustic diaphragm formed of a single layer of fabric carrying cured phenolic condensation cementing material, said diaphragm comprising stiffened vibrating portions of non-pla-niform contour and having substantially uniform thickness of not more than six thousandths of an inch throughout its stiffened vibrating portions.

1.7. The diaphragm formed of a single layer of fabric carrying cured phenolic condensation cementing material, said diaphragm comprising stiffened vibrating portions ofnon-planiform contour and having substantially uniform thickness throughout its stiffened vibrating portions.

18. The acoustic diaphragm having stiffened Warped surface central vibrating portions and relatively. flexible edge portions, said diaphragm being formed of fabric carrying incorporated cured phenolic condensation cementing material forming a substan-' tially continuous diaphragm surface and constituting at least seventy percent by weight of the vibrating portions of the diaphragm.- 7

19. The acoustic diaphragmhaving stiffened vibrating portions and relatively flexible edge portions, said diaphragm carrying incorporated cured phenolic condensation cementing material forming a substantially continuous diaphragm surface and ,constituting at least seventy percent by Weight of the vibrating portions of the diaphragm.

20. The thin substantially uniform thickness acoustic diaphragm having a diameter of more than eight inches andhaving a stiffened coned up. center portion and a'relatiyely yielding edge portion,'said diaphragm comprising a single continuous layer of fabric carrying incorporated cured phenolic condensation cementing and stiffening material to the extent of'over sixty percent by weight.

21. The acoustic diaphragm having a pro- I 22. The acoustic diaphragm having a pro- 1 jecting stifiened central vibrating portion and a relatively yielding edge portion, said diaphragm having a thickness of not more than a hundredth of an inch and being formed of fibrous material carrying incor porated cured phenolic condensation cementing material.

HARRY L. DUNCAN. 

